1. Field of the Invention
The present invention relates to image forming apparatus.
2. Description of the Related Art
Conventionally, an image forming apparatus, such as a color printer, copier, or facsimile machine, includes image forming sections for respective colors wherein the surfaces of photosensitive drums are charged and exposed to exposing devices according to image information to form electrostatic latent images, which are developed by developing devices with toners to form toner images for the respective colors. The toner images are transferred and fixed on a recording medium or paper by a fixing unit.
The transfer unit includes a plurality of transfer rollers to which a transfer voltage is applied by a voltage supply and a transfer belt for transporting the paper, and a motor for driving the transfer belt. See JP 10-63049.
If printing is started with the transfer unit not fully installed in the body of a printer, the transfer belt is not driven properly, causing poor transportation of the paper. If the transfer unit is not fully installed, keeping the contact member from connecting the voltage supply and the transfer rollers, it is impossible to transfer the toner image.
The photosensitive drums have a cylindrical shape and are rotated in sync with the running of the transfer belt to transfer the toner image to the paper. If the transfer unit is not fully installed, keeping the photosensitive drum from rotating in sync with the running of the transfer belt, it is impossible to transfer the tone image to the paper accurately. In addition, if a high charging voltage is applied to the photosensitive drum which is at rest, the high voltage is kept to be applied to a local area of the photosensitive drum, causing damage to the photosensitive drum. Thus, a mounting member is provided for each transfer roller to fully install the transfer unit in the printer body by operating the respective mounting members.
However, in the conventional printer, it is impossible to check whether the operation of each mounting member is completed. If a sensor is provided for each mounting member to determine whether the operation of the mounting member is completed, not only the structure of the printer becomes complicated but also the manufacturing cost is increased.